Php Interview Questions & Answers

1. What is PHP?

   • Answer: PHP (Hypertext Preprocessor) is a server-side scripting language designed for web development.

2. Explain the difference between echo and print in PHP.

   • Answer: Both are used to output data, but echo can take multiple parameters, while print can only take one, and print always returns 1.

3. What is the purpose of the include and require statements in PHP?

   • Answer: Both are used to include the contents of a file into another file. The difference is that if the file is not found with require, it will result in a fatal error, whereas with include, it will only produce a warning.

4. What is the difference between GET and POST methods?

   • Answer: GET appends data to the URL, while POST sends data in the HTTP request body. GET is less secure and suitable for non-sensitive data, while POST is more secure and suitable for sensitive information.

5. Explain what a session is in PHP.

   • Answer: A session is a way to store information (variables) to be used across multiple pages. It is often used to maintain user login sessions.

6. What is the difference between == and === in PHP?

   • Answer: == checks for equality only in values, while === checks for equality in both values and data types.

7. What is the purpose of the mysqli_connect() function in PHP?

   • Answer: mysqli_connect() is used to establish a connection to the MySQL database server.

8. How can you prevent SQL injection in PHP?

   • Answer: Use prepared statements and parameterized queries with either PDO (PHP Data Objects) or MySQLi.

9. Explain the use of the isset() function in PHP.

   • Answer: isset() checks if a variable is set and is not NULL.

10. What is the use of the $_SESSION superglobal in PHP?

    • Answer: $_SESSION is used to store session variables that can be used across multiple pages during a user's session.

11. What is the purpose of the header() function in PHP?

    • Answer: header() is used to send raw HTTP headers, like redirecting to another page or setting cookies.

12. Explain the purpose of the implode() function in PHP.

    • Answer: implode() is used to join elements of an array into a string with a specified delimiter.

13. What is the ternary operator in PHP?

    • Answer: The ternary operator (? :) is a shorthand way of writing an if-else statement in a single line.

14. What is the difference between array() and [] for creating arrays?

    • Answer: They both create arrays, but [] is a shorthand syntax introduced in PHP 5.4.

15. How can you prevent Cross-Site Scripting (XSS) attacks in PHP?

    • Answer: Use htmlspecialchars() or htmlentities() to sanitize user input before displaying it.

16. Explain the purpose of the __construct() method in PHP.

    • Answer: __construct() is a constructor method that is automatically called when an object is created.

17. What is the purpose of the unlink() function in PHP?

    • Answer: unlink() is used to delete a file in PHP.

18. How can you handle errors in PHP?

    • Answer: Use the try, catch, and finally blocks for exception handling, and display errors using ini_set('display_errors', 1) during development.

19. What is the use of the array_map() function in PHP?

    • Answer: array_map() applies a callback function to each element of an array and returns a new array with the modified values.

20. Explain the purpose of the json_encode() function in PHP.

    • Answer: json_encode() is used to convert a PHP array into a JSON string.

21. How can you use sessions in PHP?

    • Answer: Use session_start() to start a session, and then use $_SESSION to store and retrieve session variables.

22. What is the purpose of the file_get_contents() function in PHP?

    • Answer: file_get_contents() is used to read the contents of a file into a string.

23. What is the use of the strtotime() function in PHP?

    • Answer: strtotime() converts a human-readable date/time string into a Unix timestamp.

24. Explain the purpose of the array_merge() function in PHP.

    • Answer: array_merge() is used to merge two or more arrays into a single array.

25. What is the purpose of the $_GET and $_POST superglobals in PHP?

    • Answer: $_GET is used to collect form data after submitting an HTML form with method="get", and $_POST is used for method="post".

26. How can you use cookies in PHP?

    • Answer: Use setcookie() to set cookies, and $_COOKIE to retrieve cookie values.

27. Explain the purpose of the array_key_exists() function in PHP.

    • Answer: array_key_exists() checks if a specific key exists in an array.

28. What is the use of the array_flip() function in PHP?

    • Answer: array_flip() exchanges keys with their associated values in an array.

29. How can you upload files in PHP?

    • Answer: Use the <input type="file"> form element and move_uploaded_file() function to handle file uploads.

30. Explain the purpose of the header() function in PHP.

    • Answer: header() is used to send raw HTTP headers, like redirecting to another page or setting cookies.

31. What is the purpose of the array_filter() function in PHP?

    • Answer: array_filter() filters elements of an array using a callback function.

32. How can you create a session in PHP?

    • Answer: Use session_start() to start a session, and then use $_SESSION to store and retrieve session variables.

33. What is the difference between mysql_connect() and mysqli_connect()?

    • Answer: mysql_connect() is deprecated, and mysqli_connect() is the improved version with support for features like prepared statements.

34. Explain the use of the list() function in PHP.

    • Answer: list() is used to assign values to a list of variables in one operation based on an array.

35. **What is the purpose of the array_push() function in

PHP?** - Answer: array_push() is used to insert one or more elements at the end of an array.

36. How can you send email using PHP?

    • Answer: Use the mail() function in PHP to send emails.

37. What is the use of the array_reverse() function in PHP?

    • Answer: array_reverse() reverses the order of elements in an array.

38. Explain the purpose of the foreach() loop in PHP.

    • Answer: foreach() is used to iterate over each key/value pair in an array.

39. How can you execute a PHP script from the command line?

    • Answer: Use the php command followed by the script filename.

40. What is the purpose of the array_unique() function in PHP?

    • Answer: array_unique() removes duplicate values from an array.

41. Explain the use of the array_diff() function in PHP.

    • Answer: array_diff() computes the difference of arrays, returning the values that are present in the first array but not in the other arrays.

42. What is the purpose of the header() function in PHP?

    • Answer: header() is used to send raw HTTP headers, like redirecting to another page or setting cookies.

43. How can you connect to a MySQL database using PHP?

    • Answer: Use functions like mysqli_connect() or PDO to establish a connection to the MySQL database.

44. Explain the purpose of the array_search() function in PHP.

    • Answer: array_search() searches an array for a given value and returns the corresponding key if successful.

45. What is the use of the array_shift() function in PHP?

    • Answer: array_shift() removes the first element from an array and returns it.

46. How can you secure your PHP sessions?

    • Answer: Use session_regenerate_id(), set session.cookie_secure to true, and store sensitive session data on the server side.

47. Explain the purpose of the file_exists() function in PHP.

    • Answer: file_exists() checks whether a file or directory exists.

48. What is the purpose of the array_slice() function in PHP?

    • Answer: array_slice() extracts a portion of an array.

49. How can you create a function in PHP?

    • Answer: Use the function keyword, followed by the function name, parameters, and the function body.

50. Explain the use of the array_combine() function in PHP.

    • Answer: array_combine() creates an array by using one array for keys and another for its values.